As is well known in the art, volume phase reflection holograms are formed by exposing a photosensitive layer to an actinic interference pattern and developing the exposed photosensitive layer. The wavelength of the light diffracted by the interference fringes recorded in the photosensitive material is determined by the spacing between the fringes. Contact with water, e.g., by being stored under humid conditions, can cause changes in the spacing between the interference fringes. A change in the fringe spacing will cause a change in diffraction angle. For a reflection hologram, if the change in spacing is great enough, a wavelength shift could result which is great enough to cause the wavelength reflected to be different from that which is desired. In extreme cases, the moisture can destroy the image, whether the hologram is of the reflection or transmission type.
The copending application of Richard T. Ingwall and Herbert L. Fielding, Ser. No. 526,156, filed Aug. 24, 1983, discloses and claims photopolymerizable compositions comprising an ethylenic unsaturated monomer, preferably lithium acrylate, and a branched polyethylenine. It also is disclosed in that application that the sensitivity of the developed hologram to humidity may be substantially reduced by treating it with a zirconium compound. While this treatment is indeed beneficial, there are situations when greater resistance to humidity would be desirable.
For convenience, the disclosure of said Ser. No. 526,156 is hereby incorporated herein by reference.